1. Field of the Invention
The present invention relates to an optical component with a holder provided by fixing an optical element used in a technical field of optical communications, optical information reading and the like to a holder, and in particular, it relates to an optical component with a holder manufactured by a molding method.
2. Related Art
Although it is widely known that lenses are used in a technical field of optical communications, optical information reading and the like, most of these lenses are generally used while being previously fixed to lens holders. Although these lens fixing methods are variously provided, in particular, known is a technique of press-fitting a raw-material glass to the inside of a metallic lens holder while simultaneously molding the same in a spherical or aspherical form and integrating the lens and holder (see Japanese Patent Publication No. JP H03-265529A or, Japanese Patent Publication No. JP H03-237408A for example).
This method is far more simple than applying a metal film to the outer circumference of a single-piece lens and fixing the same to a holder by a metal solder or attaching a single-piece lens and a holder by sealing with a low-melting point glass or the like, and a low-cost highly accurate fixation between the lens and holder can be realized.
In this technique disclosed in JP H03-265529A, a projecting portion is provided on the inner circumferential surface of a through hole of a lens holder, a globular glass raw material is supported on this projecting portion, and in that condition, this glass raw material is heated and molded. Simultaneously, the glass is press-fitted to the inner circumferential surface including the projecting portion, whereby a formation of lens surface shapes by molding and a fixation to the holder are achieved.
Also, in JP H03-237408A, employed is a technique of providing a retaining portion in place of a projecting portion, supporting a plate-like glass raw material on this retaining portion, and similar to the case of Japanese Patent Publication No. JP H03-265529A, simultaneously with a surface formation by molding, press-fitting a lens to the inner circumferential surface of the holder and a step portion between the inner circumferential surface and retaining portion.
However, in the method and structure, an uneven internal stress is produced inside the lens finished by molding by a steep point of the projecting portion of the inner circumferential surface of the lens holder. When an internal stress is being produced inside a transmission optical component such as a lens, polarization properties therefore become uneven, and it cannot be used particularly for a module wherein polarization retention is required.
In addition, as a result of forming the projecting portion, during molding, a part of the glass raw material protrudes outside the molds and can cause chipping. However, this uneven protrusion which can cause defects such as chipping is, according to Japanese Patent Publication No JP 2002-6819A, eliminated by forming an annular projection different from the above-described projecting portion on the inner circumferential surface in the vicinity of an opening portion of the lens holder. However, the shape of the lens holder is complicated, and the processing cost is increased. Moreover, it is necessary to deform the annular projection by an upper metal die for molding, and it is technically very difficult to deform a part of a metal component by an expensive metal mold which is made mainly of a brittle material or ceramic.
On the other hand, in JP H03-237408A as well, a point is formed at the step portion between the retaining portion and inner surface, an uneven internal stress is similarly produced, and this may cause chipping at an edge part of the lens.
In addition, in the above-described related arts, it is necessary to match the lens holder with the glass raw material in thermal expansion coefficients (in the above-described documents, the thermal expansion coefficient of the lens holder has been made slightly greater than that of the glass raw material). Although a matching in the thermal expansion coefficients is certainly important, in parallel therewith, a matching of volume in the lens holder with the volume of the glass raw material is also important. However, if a projection and a complicated structure exist on the inner circumferential surface of the lens holder, a problem also exists such that this matching in volume is not easily achieved.